Secretion of GITSecretion of GIT

Lecture by Lecture by Dr SandeepDr Sandeep

9:30 – 10:30 am9:30 – 10:30 am13-04-0813-04-08

Salivary secretionSalivary secretion

Saliva is produced by the salivary gland at Saliva is produced by the salivary gland at the rate of 1L/daythe rate of 1L/day

The saliva helps in initial digestion of The saliva helps in initial digestion of starches and lipids by salivary enzymes, starches and lipids by salivary enzymes, dilution and buffering of ingested foods, and dilution and buffering of ingested foods, and lubrication of ingested food with mucus to lubrication of ingested food with mucus to aid smooth movementaid smooth movement

Formation of salivaFormation of saliva

Saliva is an aqueous solution whose volume is Saliva is an aqueous solution whose volume is high compared to the size high compared to the size

Saliva composed of water electrolytes, alpha Saliva composed of water electrolytes, alpha amylase, lingual lipase, kallikrein, and mucusamylase, lingual lipase, kallikrein, and mucus

Compared to plasma it is hypotonic (i.e., has Compared to plasma it is hypotonic (i.e., has lower osmolarity)lower osmolarity)

The The acinar cellsacinar cells secrete the initial saliva, which is secrete the initial saliva, which is isotonic and has same electrolyte compositionisotonic and has same electrolyte composition

The The ductal cellsductal cells modify the initial saliva. The transport modify the initial saliva. The transport mechanisms involved are mechanisms involved are

Luminal: NaLuminal: Na++-H-H++ exchange, Cl exchange, Cl-- -Hco -Hco--33 exchange, and exchange, and

HH++-K-K++ exchange exchange

The basolateral side contains The basolateral side contains NaNa++-K-K++ ATPase and Cl ATPase and Cl-- channels are present channels are present

Combined action of these transporters provides Combined action of these transporters provides absorption of Na and Cl and secretion of Kabsorption of Na and Cl and secretion of K+ + & HCO& HCO--

33 takes placetakes place

Effect of flow rate on composition of salivaEffect of flow rate on composition of saliva

Regulation of Salivary secretionRegulation of Salivary secretion

Salivary secretion is exclusively under neural Salivary secretion is exclusively under neural control by autonomic nervous systemcontrol by autonomic nervous system

Salivary secretion is increased by both Salivary secretion is increased by both parasympathetic and sympathetic stimulation, parasympathetic and sympathetic stimulation, although parasympathetic stimulation is dominantalthough parasympathetic stimulation is dominant

The parasympathetic to salivary gland is through The parasympathetic to salivary gland is through facial N. (CN VII) and glossopharyngeal (CNIX)facial N. (CN VII) and glossopharyngeal (CNIX)

Sympathetic innervation originates from T1 –T3Sympathetic innervation originates from T1 –T3

Pancreatic secretionPancreatic secretion

The exocrine pancreas secretes approximately The exocrine pancreas secretes approximately 1L/day1L/day

The secretion consist of aqueous and enzymatic The secretion consist of aqueous and enzymatic componentcomponent

Formation of pancreatic secretionFormation of pancreatic secretion

Eznymatic component of pancreatic secretion Eznymatic component of pancreatic secretion occurs from acinar cells occurs from acinar cells

Most of the enzymes required for digestion of Most of the enzymes required for digestion of carbohydrates, proteins, and lipids are secreted by carbohydrates, proteins, and lipids are secreted by the pancreas e.g., the pancreas e.g., pancreatic lipase, amylase, pancreatic lipase, amylase, proteasesproteases

The ER of the acinar cells synthesize and The ER of the acinar cells synthesize and transferred to golgi complex and then to condensing transferred to golgi complex and then to condensing vacoules, where they are concentrated and stored vacoules, where they are concentrated and stored in zymogen granules in zymogen granules

The aqueous component is secreted from The aqueous component is secreted from centroacinar and ductal cellscentroacinar and ductal cells

The initial secretion is isotonic and contains all the The initial secretion is isotonic and contains all the electrolyteselectrolytes

The apical membrane of ductal cells contains ClThe apical membrane of ductal cells contains Cl - - - - HCOHCO--

33 exchange and the basolateral membrane exchange and the basolateral membrane

contains Nacontains Na++ - K - K++ATPase and Na/H exchangerATPase and Na/H exchanger

Effect of flow rate on composition of Effect of flow rate on composition of pancreatic secretion pancreatic secretion

Regulation of pancreatic secretion Regulation of pancreatic secretion

Aqueous secretion is stimulated by the arival of HAqueous secretion is stimulated by the arival of H+ + in in the duodenum, and the enzymatic secretion is the duodenum, and the enzymatic secretion is stimulated by products of digestion (small peptides, stimulated by products of digestion (small peptides, AA, and fatty acids)AA, and fatty acids)

Acinar cells (enzymatic secretion) have receptor for Acinar cells (enzymatic secretion) have receptor for CCK and muscarinic receptors for ACh CCK and muscarinic receptors for ACh

During intestinal phase CCK is the most potent During intestinal phase CCK is the most potent stimulant for enzymatic secretionstimulant for enzymatic secretion

The I cells are stimulated to secrete CCK by the The I cells are stimulated to secrete CCK by the presence of AA, small peptides, and fatty acidspresence of AA, small peptides, and fatty acids

ACh stimulates enzymatic secretion and potentiates ACh stimulates enzymatic secretion and potentiates the action of CCK by vagovagal reflexthe action of CCK by vagovagal reflex

Ductal cellsDuctal cells (aqueous secretion) have receptors for (aqueous secretion) have receptors for CCK, ACh, and secretin, which is secreted by CCK, ACh, and secretin, which is secreted by S S cellscells of the intestine of the intestine

The chief stimulant is HThe chief stimulant is H++ in the lumen of duodenum in the lumen of duodenum

ReferenceReference

Physiology 3Physiology 3rdrd edition by edition by

Linda S CostanzoLinda S Costanzo